The present invention relates to an image scanning method according to the preamble of patent claim 1.
Such a method is employed, in particular, during aerial reconnaissance of a terrain. For this purpose, in addition to daylight cameras, an infrared camera is arranged in an airplane or in a container arranged under the airplane, said infrared camera allowing a thermal image of the overflown terrain to be recorded when visibility is poor and at night. The recorded images can be displayed to the pilot in the cockpit on a TV monitor or they can be recorded on a video recorder for later evaluation.
EP 0 503 103 B1, which was granted to the applicant, illustrates and describes an infrared imaging system which, by means of a suitably designed detector arrangement and an electronic zoom, also enables the recording of thermal images during low-altitude flight over a large scanning angle without image distortion.
The IR line scanners (IRLS=Infrared Line Scanner) used in the known imaging system join together the strip imagesxe2x80x94recorded by means of a rotating scanning mirror on a detector bankxe2x80x94without any gaps only when the scanning rate, that is to say the rotational speed of the scanning mirror, is matched to the flying altitude and flying speed of the airplane. The strip images overlap (overscan) if the flying altitude exceeds the optimum value or if the speed is below the optimum value. If the flying altitude is too low or the speed is too high, then gaps are produced between the strips. The overlap factor that is to say the overscan factor, specifies the ratio of the height of the overlapping area to the height of the image strip.
In order to obtain gap- and overlap-free recordings, either the image frequency, that is to say the scanning rate of the rotating mirror, has to be adapted to the flying altitude and the airplane speed or the airplane is forced to adhere exactly to flying altitude and speed.
Although it is actually possible to adapt the scanning rate of the scanning mirror, in terms of control technology this adaptation is difficult to control owing to the moving masses of the mirror wheel.
In addition to the overscan, a statistical image offset is also produced both in the horizontal direction and in the vertical direction on account of tolerances in the IR line scanner (jitter, synchronization problems).
The object of the present invention, therefore, is, taking account of the abovementioned fault sources, to specify a method which improves the quality of the recorded images in such a way as to enable evaluation.
This object is achieved in accordance with the defining features of patent claim 1. Further advantageous refinements of the method according to the invention can be gathered from the dependent claims.